APEX OF HOOT 157 



It is further to be observed that the cortex has 

 completely disappeared, and the peripheral layer of 

 cork is the product of the pericycle. Numerous 

 sclerenchyma-fibres are to be found scattered through 

 the secondary phloem. 



The diagrammatic Fig. 10 will illustrate the mutual 

 arrangement of the primary and secondary tissues of 

 the root. 



Apex of the Eoot. 



Type I. Using the fruit of the Sunflower in the dry 

 state, as it may be bought in seedsmens' shops, cut thin 

 median longitudinal sections of the apex of the radicle of 

 the straight embryo. The arrangement of the meristem 

 at the apex of the radicle of the embryo is similar to 

 that of the apex of the growing root, and the former is 

 chosen in this case as it is much easier to make prepara- 

 tions from it than from the growing root. The sections 

 are of little use unless they are accurately median. 



Treat the sections with potash for ten minutes or 

 more, or, better, treat with " eau de javelle " as directed 

 on p. 50 : wash with water, and mount in glycerine : 

 examine with a low power, and observe that 



1. The mass of tissue is composed of thin- walled 

 cells, arranged regularly in longitudinal rows. 



2. That these rows of cells converge towards a point 

 at some distance below the external apex of the root. 

 This is the punctum vegetationis. 



3. Note the procambium-cylinder, or formative 

 tissue of the vascular bundles, which pursues a longi- 

 tudinal course up the centre of the root. 



